Over a million Americans fail to file a tax return every year. By not filing, many of these people risk losing any refund they're owed, which averages more than $600, according to Internal Revenue Service estimates.

The law gives procrastinators three years to submit a return and claim a refund. The three-year countdown starts on the original due date. Late filers who owe no taxes don't pay any penalty, and might even be eligible to get credits beyond the money withheld from their wages.

Forgotten tax withholdings

The IRS sets minimum gross income levels below which taxpayers do not have to file a return. For example, in 2011, taxpayers under age 65 who were single and made less than $9,500, or heads of household who earned less than $12,2000, had no obligation to file.

These non-filers may have overlooked the fact that their employer withheld income tax throughout the year, which is money the IRS owes them. Additionally, their low income may qualify them for tax credits only available by filing a tax return. Citizens who did not have tax withheld also forgo the chance to receive the Earned Income Tax Credit, or EITC, by not filing.

So, just because you may not be required to file a tax return, doesn’t mean you shouldn’t. You could be missing the opportunity to get a tax refund.

Time matters with tax refunds

April 15, 2015, is the last day to file your 2011 tax return to claim a refund; if you had an extension, your deadline is October 15, 2015.

If you miss the deadline, any excess in the amount of tax you paid every paycheck or sent as quarterly estimated payments in 2011 goes to the U.S. Treasury instead of to you. You also lose the opportunity to apply any refund dollars to another tax year in which you owe income tax.

Under certain conditions the IRS will withhold your refund check. It can be used to pay any past-due student loans, child support and federal tax debt you owe. The IRS holds refund checks when the two subsequent annual returns are missing. That means you should file returns for 2012 and 2013 as soon as possible. For the 2012 tax year, the three-year grace period ends April 15, 2016.

Don't forget your credits

According to Cathy Tourbert of Pennsylvania-based Precision Tax & Business Service, tax payers who don't use a professional or online tax preparation service normally won't know what tax credits are available to them unless they read or follow tax-related news. Unclaimed 2011 tax credits represent part of the unclaimed $1 billion in the IRS's coffers. Those with low or moderate incomes may be eligible for the Earned Income Tax Credit even if they didn't have a tax bill. If your 2011 income fell below these limits, you can claim EITC by filing a 1040EZ, 1040A or 1040 return by April 15, 2015:

$13,460 ($18,470 if married filing jointly) and no qualifying children

$35,535 ($40,545 if married filing jointly) and one qualifying child

$40,363 ($45,373 if married filing jointly) and two qualifying children

$43,352 ($48,362 if married filing jointly) and three or more qualifying children

Those needing to claim refunds for the 2010 tax year have eight possible tax credits in addition to EITC they may be able to claim:

Making Work Pay Credit

Additional Child Tax Credit

American Opportunity Credit

Adoption Credit

Refundable Credit For Prior Year Minimum Tax

Health Coverage Tax Credit (Form 1040 required)

First-Time Homebuyer Credit (Form 1040 required)

Credit for Federal Tax on Fuels (Form 1040 required)

Obstacles to your tax refund

One of the hills you have to climb to claim your refund is gathering the necessary documents. If you kept your financial records, you have an easy ascent. If not, then you must build time into your filing schedule to obtain a copy of your W-2 from your employer and any 1099 forms you're missing from your bank and other payers.

The IRS can help if your document search fails. You can ask the agency for a transcript of these information returns by filing Form 4506T, "Request for Transcript of Tax Return," and checking off Box 8. Allow 10 business days for a response.

The IRS also accepts online requests (at irs.gov) and phone transcript requests (at 800-908-9946). The 1040 series of tax forms can be downloaded from the "Prior Year Returns" link on agency's "Forms and Publications" web page or ordered by calling (800) 829-3676. You have the option of e-filing or mailing a paper return. Regardless of the filing method you choose, be sure you sign, as the IRS does not issue refunds to late filers without their signature.

If you’d like to file a tax return for a previous year, TurboTax can help. Just check out our Past Year’s Products page and download the software for the tax year you need.

The above article is intended to provide generalized financial information designed to educate a broad segment of the public; it does not give personalized tax, investment, legal, or other business and professional advice. Before taking any action, you should always seek the assistance of a professional who knows your particular situation for advice on taxes, your investments, the law, or any other business and professional matters that affect you and/or your business.

Try for Free/Pay When You File: TurboTax Online pricing is based on your tax situation and varies by product. Actual prices are determined at the time of print or e-file and are subject to change without notice.

TurboTax CD/Download products: Price includes tax preparation and printing of federal tax returns and free federal efile of up to 5 federal tax returns. Additional fees apply for efiling state returns. E-file fees do not apply to New York state returns. Prices subject to change without notice.

TurboTax Mobile: Actual prices are determined at the time of print or efile and are subject to change without notice. Come back here before you file to confirm that the price has not changed, especially if it's been a while since you downloaded this app.

Pay for TurboTax out of your federal refund: A $34.99 Refund Processing Service fee applies to this payment method. Prices are subject to change without notice.

About our TurboTax Product Experts: Customer service and product support (phone or chat) vary by time of year. Phone support not included with Free Edition.

About our credentialed tax experts: Live tax advice service is available for your toughest tax questions; fees may apply. Service, experience levels, hours of operation and availability vary, and are subject to restriction and change without notice. Click here for full terms and conditions. Not available for TurboTax Business customers.

Get up to 10% on top of your federal refund: Amazon.com Gift Card offer is for federal refunds only. Limits apply ($2000 per e-card, maximum $10,000 per customer). Offer available only for TurboTax Online (except Federal Free Edition) or CD/download versions sold and shipped, or downloaded directly from Intuit or Amazon. Except as required by law, Amazon.com Gift Cards cannot be canceled, transferred for value or redeemed for cash.

#1 best-selling tax software: Based on aggregated sales data for all tax year 2013 TurboTax products.

4.8 out of 5 stars: Average based on customer ratings on TurboTax.com for TurboTax Online and CD/download products tax year 2014, as of January 2015.

Most Popular: TurboTax Deluxe is our most popular product among TurboTax Online users with more complex tax situations.

TurboTax CD/Download priority phone support: Priority phone support for TurboTax CD/Download Premier and Home & Business is accessible exclusively via the TurboTax.com Help Center.

Benefit Assist: After you file, TurboTax automatically shows you a full list of government benefits you may qualify for, like Food Stamps or reduced phone & utilities. Plus, we help you apply, saving you time and making it easier than ever to get more money! Estimate based on calculation of Benefit Assist users from tax year 2013 and published reports of average benefit and savings amounts from federal and state programs. Actual amounts and qualifications based on your individual situation; some individuals will not qualify. Feature may not be available for all customers.

Simplified State Experience: New, simplified state tax preparation available for most filers.

Eligibility for $25 cash back for returning Deluxe customers: Customers who have completed their 2013 taxes in TurboTax Deluxe (CD or download), and have completed their 2014 taxes in either TurboTax Premier or TurboTax Home & Business (CD or download), and apply here before 11:59PM PDT April 20, 2015, are eligible for $25 back. 2014 TurboTax Advantage users are ineligible for this offer. Terms and conditions are subject to change without notice.

$0 Upgrade Offer: Valid for customers who filed their 2013 taxes with TurboTax Deluxe (CD or download), completed prior year data transfer this year, and encounter an upgrade to either 2014 TurboTax Premier or 2014 TurboTax Home & Business (CD or download). Valid February 6, 2015 through April 20, 2015. TurboTax Advantage users are ineligible for this offer. This offer may not be combined with our $25 cash back offer. Terms and conditions are subject to change without notice.